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4th year medicine > PH and EBM > Flashcards

PH and EBM Flashcards

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1
Q

PICO

A

patient/ population
Intervention/ treatment
Comparison/ alternative treatment
Other relevant clinical info

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2
Q

types of observational study

advantages and disadvantages

A

observational:

  • ecological
  • cross sectional
  • case-control
  • cohort study

advantages:

  • ethics (can’t force a group to smoke)
  • can use very large groups

disadvantages:

  • biases
  • confounding (links an exposure with an outcome)
  • reverse causality
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3
Q

cohort study

A

DONT HAVE ANY DISEASE AT START - see who develops disease with risk factors

  • exposure to defined factors measured at baseline
  • any new incidence of disease
  • high and low exposure individuals compared
  • calculate RISK RATIO
  • prospective or retrospective

advantages:

  • reduce reverse causality
  • reduces selection bias
  • allows testing of multiple outcome
  • better confounder control

disadvantages:

  • retrospective: recall and interviewer bias, reverse causality
  • prospective: LONG, LOSS TO FOLLOW UP bias
  • inefficient for rare diseases
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4
Q

cross-sectional study

A

SNAPSHOT OF PREVALENCE

  • shows prevalence of disease in population at snap shot moment,
  • good for measuring true burden of disease
  • measure risk factors,
  • can’t measure incidence, susceptible to reverse causality
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5
Q

case-control study

A

WHAT IS CAUSE OF THE OUTCOME

  • recruit available cases and a comparable control group
  • sample determined by outcome
  • RETROSPECTIVELY assess exposure to potential risk factors - compare case and control
  • if exposure more common in cases, risk factor associated with increased disease
  • presented as ODDS RATIO

advantages:

  • only study comparing groups defined by outcome
  • good for RARE CONDITIONS
  • can test for multiple exposures

disadvantages:
- reverse causality
- selection bias: when selecting control group, choose suitable population, not one which would have higher/lower associations to exposure
- measurement bias:
recall bias- cases more likely to recall exposure as they understand disease
interviewer bias - can cause cases to recall more exposure

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6
Q

systematic review

A
  • all relevant evidence on a given clinical question
  • minimise biases and random errors
  • highest quality of evidence
  • much cheaper and quicker than RCTs

disadvantages:

  • only as good as the studies they’re done on
  • reporting biases:
  • -> publication bias - statistically significant are more likely published
  • -> time lag - big studies published quicker
  • -> language - English get published quicker
  • -> multiple publication - big studies may be published in multiple places
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7
Q

p value

A

the probability of the observed results occurring just by chance, if the null hypothesis was true

very low p-value indicates strong evidence against the null hypothesis (differs in outcome to control)

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8
Q

risk ratio vs odds ratio

A

risk ratio: out of total number of people in the study

odds ratio: out of unaffected patients

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9
Q

sensitivity vs specificity

A

sensitivity:
true positive rate - probability of a positive test in people with disease (proportion of all those with the condition)

specificity:
true negative rate - prob of negative test result in people without disease

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10
Q

primary prevention definition

A

prevent the onset of disease

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11
Q

secondary prevention

A

early identification and treatment of disease

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12
Q

tertiary prevention

A

rehabilitate people with established disease

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13
Q

prevention paradox

A

large number of small risk cases may get disease, but population interventions may provide little to individuals

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14
Q

R number

A

effective reproduction rate - number coming from one case

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15
Q

R0

A

basic reproduction number R0 =
probability of effective contact x number of contacts x duration of infectiousness

better for planning for infectious diseases

(in a wholly susceptible population- scenario with no immunity)

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16
Q

cost effectiveness

A

cost per clinical effect

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17
Q

cost utility

A

cost per QALY

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18
Q

SMR ratio calculation

A

SMR =

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19
Q

example q:

condition present:
test +ve: 60
test -ve: 57
total: 117

condition absent:
test +ve: 1
test -ve: 400
total: 401

total +ve: 61
total -ve: 457

total people:
518

calculate sensitivity, specificity, positive predictive value, negative predictive value

A

sensitivity: 60/117
specificity: 400/401

positive predictive value: 60/61

negative predictive value: 400/457

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20
Q

positive predictive value

A

probability of having disease if you test positive

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21
Q

negative predictive value

A

probability of not having disease if you test negative

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22
Q

inverse equity hypothesis

A

new health interventions are initially adopted by wealthy/ educated, initially increasing inequalities as poorest/ less educated lag behind on uptake of the new health intervention

example: traffic light labelling of foods sold pre-packaged

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23
Q

which mechanism is bias reduced by with using big groups (e.g. school) instead of individuals

A

contamination

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24
Q

what aspect of trial quality is always feasible when comparing treatments in an RCT

A

allocation concealment

not: blinding (on either side), follow up

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25
best available evidence in order
1. systematic review 2. RCTs 3. cohort studies 4. case-controlled studies 5. background info
26
ecological study
WHAT IS THE EXPOSURE CAUSING - average exposure plotted against rate of outcome - association btwn them - environmental or social exposures at population levels - disadvantages: ecological fallacy difficult to control confounding dependent on previously collected data
27
what is ecological fallacy?
disadvantage of ecological studies: the assumption that average characteristics apply to individual e.g. smokers get cancer
28
RCTs
- interventional study - two arms one group exposed - participants consent advantages: - evidence of causality - best confounder control - allocation concealment reduces selection bias - blinding reduces measurement bias disadvantage: - sample size needs to be large enough - selection bias - performance bias - detection bias - attrition bias (unequal loss of participants)
29
meta analysis
statistical analysis - combing results of independent studies - similar intervention, similar outcome, similar populations fixed (common) effect: - assumes true effect is the same in each study. - the only variation in estimates is sampling error. (assumes all studies are trying to show the same thing- homogeneity) - less weight given to small samples random effects: - estimates mean effect (assumed that the true study effects vary- not showing same effect - heterogeneity). - info from small studies matters more heterogeneity: - suggests treatment effect is context dependent (all studies not showing same effect) funnel plots asymmetry: - publication/reporting bias, poorer quality studies --> extreme treatment effects
30
what methods are used for qualitative studies
for helping understand why something happened - observations - interviews - focus groups - documents - oral history
31
what data analysis is used for qualitative studies?
1. familiarisation with data 2. coding (repeated ideas) 3. searching for themes 4. reviewing themes 5. defining and naming themes 6. writing up
32
performance bias
affects RCTs systematic differences in the care provided to members of different study groups other than the intervention
33
detection bias
affects RCTs systematic differences btwn groups in how outcomes are determined
34
attrition bias
affects RCTs if the numbers lost to follow up are not the same in each group
35
intention to treat analysis
done to avoid the effects of crossover and dropout comparison of the treatment groups that includes all patients as originally allocated after randomization
36
per protocol analysis
instead of intention to treat analysis comparison of treatment groups that includes only those patients who completed the treatment originally allocated
37
reporting biases
- publication bias- statistically significant are more likely to be published - time lag - big studies published quicker - language - English studies quicker - multiple publication - in bigger studies
38
forest plots
fixed or random model pulled odds ration with 95% CI tails diamond: overall odds ratio in the middle with overall 95% CI on the ends
39
funnel plots
to show whether there is publication bias - used in SRs and meta-analysis - asymmetric (if part not filled in, they haven't been published --> publication bias)
40
prevalence calculation
total patients with disease in population individuals w disease / total population at risk
41
incidence
new cases in given period / population at risk initially disease free
42
incidence rate
(# new cases of disease) / (population at risk) x time interval)
43
risk
patients w disease / population
44
risk ratio
risk of outcome occurrence in exposed / risk of outcome occurrence in unexposed likelyhood of disease with exposure compared to without exposure- strength of association not causality RR> 1 exposure predisposes outcome RR<1 exposure protects against outcome
45
risk difference
risk of outcome in exposed - risk of outcome in unexposed
46
number needed to treat
1/ risk difference number of patients that would need to be treated to prevent one case of the disease
47
odds
patients with disease / patients without disease
48
odds ratio
odds of having disease in exposed / odds of having disease in unexposed
49
null hypothesis
- no difference btwn case population and control population | - study aims to disprove null hypothesis
50
p-value
- the probability that differences in observed data would have occurred by chance - small p-value (p<0.05) = greater evidence against null hypothesis
51
incremental cost-effectiveness ratio
= C/E = (Ct - Cc)/ (Et - Ec) TOTAL COST OVER QALY ``` C= cost E= effectiveness t = treatment c = comparator ``` compares treatment to comparator (next best)
52
Quality Adjusted Life Year (QALY)
= (time spent in healthy state) x (quality of life weight)
53
standard mortality ratio
= (# observed deaths / # expected deaths) x 100 - ratio of observed deaths to expected deaths - SMR 100 = study pop has same number of deaths as standard pop - SMR > 100 more than expected # of deaths
54
statistical power
probability of correctly rejecting null hypothesis when in truth the treatment has an effect
55
net monetary benefits
= (E x lamda) - C ``` E= cost lamda = willingness to pa for QALY C = cost ```
56
95% CI
range of value within which we are 95% confident that the true population value lies
57
+ve likelihood ratio
probability of a positive test in people with the disease/ probability of a positive test in people without the disease = sensitivity/ (1-specificity) used with layers monogram
58
accuracy
(true positives + true negatives) / all results
59
SpPin
when a test has a high specificity a positive result rules IN the target disorder
60
SnNout
sensitivity - when a test has a high sensitivity a negative result rules out the target disorder
61
spectrum bias in diagnostic testing
the types of patients recruited to the study
62
work up bias in diagnostic testing
do all patients get both diagnostic and gold standard tests
63
improving public health by health protection
``` infectious disease - childhood vaccination - immunisation environmental hazards emergency response to infectious disease outbreaks ```
64
improving public health by health promotion
- develop primary promotion programme - health inequalities - behaviour change
65
improving public health by health services
- secondary prevention programmes e.g. screening - healthcare quality - health policy
66
proportionate universalism | - what is it the solution to and what is it?
solution to prevention paradox providing service universally but with increased intensity on disadvantaged
67
vaccination programme types
- universal rolling - give vaccine continuously to everyone of certain age when they reach it - universal catch-up - give vaccine to everyone in pop within a certain age range with a fixed time period - targeted - aimed at people who are high risk
68
types of vaccine
live vaccine: - MMR, BCG, rotavirus, polio, influenza - strong immune response - can be administered via mucosal route - mild infection after - must be maintained alive (cold chain) conjugate vaccine: - HiB, men C - development of immunity to non-protein material - smaller response toxoid: - diphtheria, tetnus - no risk of infection subunit - pertussis, MenB
69
health inequality vs health inequity
health inequality: differences in health health inequity: unjust difference
70
harms of screening
- false negatives/ false reassurance - over detection - false anxiety - can increase incidence (picking up more less serious cases) - length time bias - leaves out poor prognosis (cause treated quickly)
71
healthy screened effect
people who come for screening tend to be healthier than those who don't

4th year medicine (8 decks)

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